8.1.4 Differential Manchester Coding

The 802.5 standard specifies that Differential Manchester coding is used for transmitting data on the ring. With this encoding technique, every bit is comprised of a half-bit time signal at a low or high polarity and other half-bit time signal at the opposite polarity. The mid-bit transition is for clocking only. The direction of the signal′s voltage transition will change whenever a ″0″ bit is transmitted and will stay the same for a ″1″ bit transmission. Therefore, each bit consists of two half-bits at opposite polarity. This scheme is said to be DC balanced. Figure 80 shows the principles of the Differential Manchester coding.

Figure 80. Differential Manchester Coding

To understand the reasons for DC balanced signalling, consider a baseband transmission using a simple transmission code such as NRZ (Non-Return to Zero) where during the transmission a ″1″ bit is represented as a + voltage and a ″0″ bit is represented as a - voltage (opposite direction of the ″1″ bit). Depending on the bit stream that is being transmitted with NRZ, it is possible that the line may spend on average more time in one voltage level than the other. In other words, the signal would be electrically unbalanced. Since the physical wire has capacitance, the unbalanced signal causes the wire to develop a constant DC voltage across the transmission media, which in turn, causes the transmission media to distort the signal. This phenomenon is called ″baseline wander″ and the effect of that is to increase the interference caused by one pulse with a subsequent pulse on the transmission media. The result of this interference is that the signal is ″smeared″ so that the end of one bit, or a group of bits, overlap with the start of the next. This makes an unbalanced coding technique such as NRZ or NRZI unsuitable for high speed transmissions such as 4 or 16 Mbps token-ring networks. The use of Differential Manchester coding technique in token-ring networks would allow us to overcome this problem and have a DC balanced transmission on the media.

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IBM 8260 manual Differential Manchester Coding
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8260 specifications

The IBM 8260 is a significant entry in the realm of enterprise servers, recognized for its performance, scalability, and robust features designed to cater to demanding business environments. It primarily serves as a high-capacity server for large organizations, capable of handling extensive workloads and complex applications without compromising speed or efficiency.

One of the standout features of the IBM 8260 is its powerful processing capabilities. It typically comes equipped with multiple processor units based on the IBM POWER architecture, which is renowned for its high-performance computing. This architecture allows the server to execute numerous simultaneous tasks, making it ideal for environments that require multitasking and high throughput.

Memory capacity is another key characteristic of the IBM 8260. Depending on the specific configuration, it can support substantial amounts of RAM, ensuring that applications can run effectively without the bottlenecks often associated with data-intensive tasks. This is crucial for enterprises that rely on real-time data analytics, large database management, and resource-heavy applications.

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Connectivity is also a prominent feature of the IBM 8260. The server includes advanced networking capabilities, supporting various protocols and technologies that facilitate fast data transfer and communication between devices. This enhances overall network performance, essential for businesses that depend on cloud computing and distributed computing environments.

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In conclusion, the IBM 8260 stands out in the competitive server landscape due to its high processing power, extensive memory and storage options, advanced connectivity, reliability features, and robust management tools. Such attributes make it a viable choice for organizations seeking to enhance their IT infrastructure and streamline their operations effectively.
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